1. Field
Exemplary embodiments relate to data transmission technology, and more particularly, to data transmission technology using a relay server.
2. Discussion of Related Art
Peer-to-peer (P2P) technology enables users to share various information and content by directly connecting individual terminals. The P2P technology has initially been used as means for enabling users to unlawfully share music files and video files with each other on the Internet. However, recently, the P2P technology has been utilized in various services such as file transmission between clients in a messenger system, audio data transmission in Internet telephony, and the like. The number of fields using the P2P technology is increasing.
If a direct connection between clients is not possible because the clients exist in private networks in the P2P technology, a method of relaying data using a relay server is used. At this time, a user datagram protocol (UDP) relay server is used when UDP data is relayed, and a transmission control protocol (TCP) relay server is used when TCP data is relayed. However, the data transmission method using the relay server in the related art has the following problems.
The first problem is that a client should be periodically connected to a specific server so as to establish a connection to a service and exchange data (a message, a file, or the like) with other clients. For this, many service providers configure login servers so that the clients can access services when the clients are authenticated by the login servers. At this time, the client maintains a TCP connection to the login server, and recognizes a state in which a P2P service is available through the TCP connection. However, a heavy load is placed on the server when the clients continuously maintain TCP connections through the login server.
The second problem is that each client should transmit data to a second client through the relay server after establishing a connection to the relay server (the TCP relay server or the UDP relay server) if a direct connection between clients is not possible because the clients exist in private networks. However, because the TCP relay server relays only TCP data and the UDP relay server relays only UDP data, the client does not transmit data through the UDP relay server in an environment where a UDP connection is not possible. When types of relay servers connected to the clients are different from each other, data transmission may be impossible.
The third problem is that data transmission is not directly ensured because each client is not in a state in which a direct connection to a second client is established when data is relayed through the relay server between the clients. That is, there is a problem in that the reliability of data transmission is not ensured because it is not possible to directly determine whether or not a second client has successfully received its own sent data.